This application is a 371 of PCT/JP99/02978 filed Jun. 3, 1999.
The present invention relates to an epoxy resin composition for semiconductor encapsulation which is effective in mitigating molding failures (chip tilting) occurring during resin encapsulation by transfer molding, etc., and is capable of imparting high reliability, and to a semiconductor device obtained with the composition.
Semiconductor elements such as transistors, ICs and LSIs have conventionally been encapsulated in plastic packages represented by, for example, dual inline packages (DIPs) to produce semiconductor devices from the standpoints of protection from the surrounding atmosphere and facilitating the handling of semiconductor elements.
As the prior art encapsulation materials used for such plastic packages, epoxy resin compositions are used.
However, the semiconductor devices obtained by encapsulating semiconductor elements with conventional encapsulation materials by transfer molding or another molding technique have a drawback of poor reliability. This is because there are cases where the resin flow during molding may slightly shift the semiconductor element placed within the mold in its original right position or may deform the gold wires disposed by wire bonding.
The present invention has been made in view of such circumstances, and objects of the present invention are to provide an epoxy resin composition for semiconductor encapsulation which does not cause the chip tilting attributable to resin flow during resin encapsulation, such as semiconductor element shifting and gold wire deformation, and is capable of yielding highly reliable semiconductor devices, and a semiconductor device obtained with the epoxy resin composition.
For accomplishing the above objects, the first aspect of the present invention resides in an epoxy resin composition for semiconductor encapsulation which comprises an epoxy resin, a phenolic resin, a hardening accelerator and an inorganic filler, said epoxy resin composition having the following properties (X) to (Z):
(X) the viscosity thereof as measured with a flow tester at 175xc2x0 C. is from 50 to 500 poise;
(Y) the minimum melt viscosity thereof as determined from the temperature dependence of viscosity thereof as measured with a dynamic viscoelastic meter at a shear rate of 5 (1/s) is 1xc3x97105 poise or lower; and
(Z) the ratio of the viscosity thereof as measured at 90xc2x0 C. (Z1) to that as measured at 110xc2x0 C. (Z2) both with a dynamic viscoelastic meter at a shear rate of 5 (1/s), (Z1/Z2), is 2.0 or higher.
The second aspect of the present invention resides in a semiconductor device produced by encapsulating a semiconductor element with the above epoxy resin composition for semiconductor encapsulation.
The present inventors made intensive investigations on epoxy resin compositions as encapsulation materials mainly with respect to the viscosity characteristics thereof in order to prevent the chip tilting occurring upon resin encapsulation by transfer molding, etc., such as semiconductor element shifting or gold wire deformation, to thereby obtain highly reliable semiconductor devices. As a result, the present inventors have found that when an epoxy resin composition is regulated so that the viscosity thereof as measured with a flow tester at 175xc2x0 C. [property (X)], the minimum melt viscosity thereof as measured with a dynamic viscoelastic meter [property (Y)], and the ratio of the viscosity thereof at 90xc2x0 C. (Z1) to that at 110xc2x0 C. (Z2) [(Z1/Z2); property (Z)] are within respective specific ranges, then the encapsulation problems are prevented from occurring and semiconductor devices having high reliability can be obtained, and have reached the present invention.
By regulating the content of the inorganic filler as a component of the epoxy resin composition for semiconductor encapsulation to a value within a specific range, the packages formed from the composition can decrease water absorption. As a result, the semiconductor devices produced with the composition can retain high reliability after mounting.
Furthermore, when the hardening accelerator as a component of the epoxy resin composition for semiconductor encapsulation is microcapsules containing a hardening accelerator which have a core/shell structure composed of a core comprising the hardening accelerator and a shell comprising a synthetic resin with which the core is covered, the components of the epoxy resin composition can be melt-kneaded for a longer period than conventional ones and at a higher temperature. As a result, it is easy to obtain an epoxy resin composition having the viscosity properties (X) to (Z) described above.